There are earlier known different devices for measuring strain in or the inclination of a cable immediately outboard of a floating vessel. As to the strain measuring equipment, the following references may be mentioned:
U.K. Pat. No. 743,862 which shows a cable holding, braking or winding arrangement comprising two pulleys mounted on a common rotatable carrier;
West German Auslegungschrift No. 21.41.095 (U.S. Pat. No. 3,802,258) which concerns a cable paying out arrangement having resilient members to compensate for sudden strain changes and to indicate the cable strain;
U.K. Pat. No. 1,241,776 which shows a load indicator for mooring lines in which strain gauges are used to detect the strain forces, while the final strain is found by comparing the measured result with an ideal catenary line calculation; and
U.K. Pat. No. 1,422,946 (U.S. Pat. No. 3,913,396) also relates to a mooring line system in which the tension in several mooring ropes are measured and compared in a monitoring station which also may give a visual display of the result.
As for devices for measuring the inclination angle, relative to vertical, at which the cable leaves a vessel, no references are mentioned, but all known equipment include large mechanical arms which touch the cable and are guided by it. All of these earlier techniques involve major deficiencies, such as, e.g., being impractical in tough marine environments, being unreliable, being difficult to adjust, and providing measurement which precision is much lower than desired.
A purpose of the present invention is to provide a method according to which either or both of the total cable stress and the inclination angle of the cable is found without use of complicated mechanical arrangements which are sensitive to variable field conditions. A further purpose is to provide methods and arrangements which allow compensation for influences from the accelerations of the ship on the measured values.